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Date: Tue, 28 Jul 2026 11:15:09 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Richard Chang <richardycc@google.com>
Cc: Minchan Kim <minchan@kernel.org>, Sergey Senozhatsky
 <senozhatsky@chromium.org>, Martin Liu <liumartin@google.com>,
 linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm/zsmalloc: fix release order of locks in
 zs_page_migrate()
Message-Id: <20260728111509.7662e385aea0b055d2066e1f@linux-foundation.org>
In-Reply-To: <20260728055333.421080-1-richardycc@google.com>
References: <20260728055333.421080-1-richardycc@google.com>
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On Tue, 28 Jul 2026 05:53:33 +0000 Richard Chang <richardycc@google.com> wrote:

> In zs_page_migrate(), locks are acquired in the following order:
>   1. write_lock(&pool->lock)
>   2. spin_lock(&class->lock)
>   3. zspage_write_trylock(zspage)
> 
> However, upon successful page migration, they were being released in
> forward acquisition (FIFO) order:
>   1. write_unlock(&pool->lock)
>   2. spin_unlock(&class->lock)
>   3. zspage_write_unlock(zspage)
> 
> Fix the unlocking order to release locks in strict reverse (LIFO)
> order of acquisition:
>   3. zspage_write_unlock(zspage)
>   2. spin_unlock(&class->lock)
>   1. write_unlock(&pool->lock)
> 
> Releasing locks in reverse order of acquisition adheres to standard
> kernel locking hygiene, prevents potential lock ordering and lockdep
> inconsistencies.
> 

Thanks.

Does this actually fix a lockdep splat?  If so, is a link available?